1. Field of the Invention
The present invention relates to a display method of an emission display apparatus using an organic EL device, and more particularly, to a display method of an emission display apparatus which features a control method of a pixel structure.
2. Description of the Related Art
In a flat panel image display apparatus (flat panel display) such as an organic EL display, when the same still image is displayed for a long period of time, a phenomenon called “sticking” occurs. The term “sticking” herein employed means that only a part of a display screen is degraded (reduction of emission luminance) to generate a residual image (after image) which can be visually recognized. The sticking is liable to occur in an edge portion or the like of a still image.
In organic EL displays having a plurality of subpixels of different emission wavelengths, there are many cases where the degradation characteristics are not identical for each emission color. In addition, because the content of an image displayed on the display screen is not uniform, the degradation is liable to proceed locally. In this case, because the reduction in emission luminance differs for each color, there occurs the so-called “color shift” in which the white balance is deviated, whereby a white image appears to be colored.
Further, examples of factors for accelerating the degradation include display of a fixed pattern, nonuniformity of emission times of respective subpixels, time period in which light is emitted, ambient temperature, and magnitude of emission luminance, which are responsible for the sticking phenomenon.
In order to suppress the sticking phenomenon, it is preferred to improve emission lifetimes of constituent materials. However, it is difficult to say that the sticking phenomenon can be sufficiently suppressed only by improving the materials. Documents disclosing technologies for suppressing the sticking phenomenon are described below.
Firstly, there is disclosed a technology of controlling the emission luminance of each color based on an accumulated emission time to ensure uniform progression of degradation of respective colors, thereby obscuring the sticking (Japanese Patent Application Laid-Open No. 2000-356981).
Secondly, there is disclosed a technology of detecting the luminance of a pixel degraded due to high luminance emission and adjusting the luminances of the other pixels to the luminance of the degraded pixel, thereby obscuring the sticking (Japanese Patent Application Laid-Open No. 2001-175221).
However, according to the technology disclosed in Japanese Patent Application Laid-Open No. 2000-356981, the luminance of the entire display screen is merely reduced based on the display time length, and hence occurrence of the “sticking” phenomenon cannot be essentially avoided. Moreover, the technology disclosed in Japanese Patent Application Laid-Open No. 2001-175221 has an effect of suppressing the color shift because the luminance of the other pixels is adjusted to the luminance of the pixel degraded due to high luminance emission. However, there is no effect of suppressing the luminance degraded itself of the pixels. Further, an additional sensor is required for detecting the luminance, thereby resulting in an increase in the production cost and a reduction in resolution.
In an organic EL display, when the same still image is displayed for a long period of time, only a part of a display screen is degraded, thereby causing the sticking phenomenon. Further, in organic EL displays having a plurality of subpixels of different emission wavelengths, since the degradation characteristics are not identical for each emission color, there is caused a color shift in many cases.